Significance Better understanding of how our visual system develops, adapts, and integrateswith our other sensory systems. Objectives One of the central problems of visual science is to establish how the numerous areas together form our seemingly unified visual experience. In my work, I attempt to decipher the mechanisms and consequences of the hierarchical connection between two specific areas in the visual cortex of the rhesus macaque (M. mulatta). These two areas (MT and MST) form a perfect example of serial processing, and we already know a great deal about how they are orgainized and what kind of information they represent. Both are specialized for the analysis of visual motion, but MST (the later stage of processing) appears to represent much more complex aspects of image motion, such as rotation, expansion, and contraction. Using a combination of behavioral and physiological approaches, we are both exploring the mechanisms by which the simpler representation in MT is transformed into the more complex one in MST, and testing the hypothesis that the more complex representation in MST is uniquely involved in more complex visual tasks. To do this, we train monkeys on tasks demanding the analysis of visual motion, and precisely measure the signals in these cortical areas with single cell recording techniques, or alternatively, we perturb the signals in these areas using very small electrical currents, and measure the effects on the animals behavior. Results We have been exploring a specific complex motion task, recovering self-motion from image motion, and have recently demonstrated large effects of microstimulation of both areas MT and MST on this task. This shows that higher areas in cortex are directly involved in this task. Future Directions Future experiments will be probing the mechanisms of this involvement.